When the cart accelerates down the track the distances between ticks will grow constantly. When it encounters an obstacle in the track the cart will be slowed down momentarily. This will be made visible on the tape as a shorter distance between the ticks as the cart was slowed down momentarily.

Friction introduces a force that will retard the motion of the system. To eliminate its effects one needs to add a force to the system that cancels it out. In the case of the ramp this might be achieved by offsetting the angular measurement of the ramp or introducing a mass that is not used in the calculations.